Regarding the Ring:
This man speaks the truth. Nurburgring is ridiculous enough as it is in Forza, if a 100% realistic version is even narrower I wouldn't want it. It's already borderline useless for races. Safe overtaking places are sometimes minutes apart, and the speeds are so high that even a slight touch means it's over for both of you. Every time we race it online it becomes a game of follow the leader until either:
a) the guy in front of your cracks under pressure and crashes, so you pass.
b) you crack under pressure and try to overtake. Both of you crash 75% of the time.
That's not a big problem with other games, like GTR Evo, and heck, it's on Steam!
I must've run hundreds of laps around the ring in the CCGT and Spyker online and offline, and once the field has sorted itself out through the first corner (goes surprisingly well), the racing is generally clean AND aggressive from there on.
Of course, the racing does come down to skill, and who is driving smarter (it's not rare to see the Spykers holding up C6.R's through the first 'third' of the lap). And the cars that hang on through the slower corners and are absolutely planted through the faster ones generally come out on top (even if it means you're sometimes losing 15km/h on the straight, I think it's worth it), but it's always up to the driver to get the most out of the car.
Take this video for references (I can't tell you the name/number of every corner):
http://www.youtube.com/watch?v=y-1sdSoj2Ec
1:00 is always good fun in a pack, because half the cars will stay to the inside, and the others will drop out wide for a better run into the right-hander. Then coming off the exit you can cleanly pass many cars.
1:12 is another great spot for passing. It's possible for someone to dive up the inside, and make it through the next left-hander, and then be passed by the person who took th ideal racing line.
1:28 makes for interesting racing, rewarding the brave driver who can easily make up a position by going around the outside. This takes balls, and a car that handles well at higher speeds (the CCGT is best in this aspect I think), and only rarely will you make contact because the racing lines are so different. It should be noted you need a good tow and a 'run-up' to pull it off though.
1:45 and another great opportunity for the brave, ballsy driver with the stable car. Attack the corner, stick two wheels on the grass if need be, and you should manage to avoid all contact, because the other cars will drift wider, earlier than you. Of course, if you're not in front, you're screwed for the next corner, which brings me onto:
1:50. A good, deep braking zone, and if you can carry some brake into the corner better than another driver, you've got them easier than tempting a fat person with cake. However, a less-than-perfect exit puts you in danger for the next 20 seconds.
2:09, again, is great for the ballsy driver. If you can get your car turned in well, you can carry immense pace through this corner, and odds are since you'll have to 'turn in' much earlier, you can easily make it through cleanly.
2:13 to 2:20 is a complex series of corners, with millions of alternate racing lines. As a result, it's astoundingly easy to fly through there in a pack without even scratching your Koenigsegg. That also means good overtaking potential.
2:32-2:38, great for passing. Get good drive out of the first one (odds are you've got a tow into it) and you can nail them into the second one.
2:43, a continuation of the last few corners, a mildly heavy braking zone followed by a slowish corner is great overtaking potential.
3:00, epic. There's a million ways around someone through this 30-second sequence. Honestly, if you can't find a way past a car in those 30 seconds, you deserve to finish second.
3:36; braking zone (and following corner exit) ripe for overtaking
4:18, see above
4:29: see above
4:47 tricky left-hander often leads to cars running wide at 4:50, great opportunity.
5:00-5:50 this section can sometimes be tedious, but if you're stuck behind someone, try a different line. That section is actually quite forgiving if you're not 100% on the racing line, and you WILL get the opportunity to put 2 wheels on the grass and stick the nose up inside another car. Then it's possible to run side-by-side for a LONG time.
5:54. If you have balls, not is the time to use them. stay committed to that corner, and bam instant massive speed advantage on the next straight.
6:04 tricky corner entrance, and if done correctly, it's easily a second off your lap time. And sometimes even 3-4 more cars behind you.
6:13, attack this and there's a lot of speed to be gained. This corner is fairly forgiving, and yet it rewards alternate (including aggressive) lines. Use it.
The series of right-handers coming onto the long straight can be used to great effect; sometimes cars will got for the highest corner speed, others the highest exit speed, other still the highest entry speed. Use this. Then grab a tow and take them down (up?) the straight.
I don't need to say how good the last few corners are for overtaking (coming off the straight is sometimes like a game of chicken with the grass/wall/etc though). Admittedly, the last corner is almost always useless, but get a good exit and you're set for turn 1.